1. Technical Field
The present invention generally relates to interferometric testing devices and, more particularly, to a holder for a lens under test in an in-line hologram interferometric test apparatus.
2. Discussion
In-line holographic testing employs a hologram interposed in space relation to an interferometer and a lens under test. The interferometer projects a beam of radiation through the hologram towards the lens under test. As the beam propagates through the hologram a wavefront is created which converges to a focal point at a pre-selected focal length from the hologram. From the focal point, the beam diverges to the lens under test.
When the lens under test is correctly positioned with respect to the interferometer, hologram, and focal point, the wavefront is reflected back through the hologram to the interferometer. The hologram converts the wavefront back into an aspherical beam suitable for interference patterning by the interferometer. As such, any abnormalities or errors associated with the lens under test can be detected and analyzed by the interferometer's analysis system.
During this testing, it is critical to correctly position the lens under test with respect to the interferometer in order to accurately and precisely reflect back the aspherical wavefront. The exact position for the lens under test is often dictated by the characteristics of the hologram itself. To properly locate to lens, translational positioning of the lens must be performed in the X, Y and Z planes and rotational positioning of the lens must be performed in tip (about a horizontal axis) and tilt (about a vertical axis).
According to the prior art, the lens under test is secured to a fixture which is initially positioned to the interferometer focus. The lens under test is then iterated to the desired position using slides, scales, and spacers. This technique requires a large degree of optician skill and experience to position the lens under test quickly and accurately. Furthermore, rotational positioning of the lens under test according to the prior art is achieved largely through trial and error.
Accordingly, there is a need in the art for an apparatus and method for quickly and accurately positioning a lens under test relative to an interferometer and hologram in an in-line hologram interferometric test apparatus.